1. Field of the Invention
The subject invention generally pertains to a refrigerant system and more specifically to the coil configuration of a wound heat exchanger coil.
2. Description of Related Art
Many air conditioning systems, such as split-systems and/or heat pumps, fundamentally include an indoor heat exchanger, an outdoor heat exchanger, a compressor and an expansion device that are connected in series to comprise a refrigerant circuit. As the compressor forces refrigerant through the circuit, compression and expansion of the refrigerant respectively raises and lowers the temperature of the refrigerant. The refrigerant then absorbs or expels heat to the external surroundings of the heat exchangers. For example, in a cooling mode, relatively cool, lower pressure refrigerant passing through the indoor heat exchanger (operating as an evaporator) cools the indoor air (directly or via an intermediate fluid), while relatively hot, higher pressure refrigerant delivered to the outdoor heat exchanger (operating as a condenser) expels heat to the outside ambient air (or water). With some systems, generally reversing the direction of part or all of the refrigerant flow through the circuit places the system in a heating mode to warm the indoor air or temporarily places the system in a defrost mode. In the defrost mode, the circuit directs relatively hot, higher pressure refrigerant to the heat exchanger that was previously operating as the evaporator, and thus thaws frost that may have accumulated on that heat exchanger.
Outdoor heat exchangers often comprise several wound tubes to provide several coiled circuits that are arranged directly above each other so that the coiled tubes become the perimeter of a larger tubular assembly. Two vertical manifolds connecting the ends of each wound tube places the coiled circuits in parallel flow relationship with each other. The tubes usually have external fins (e.g., spine fins) to promote heat transfer and thus improve the overall efficiency of the air conditioning system.
However, as consumers demand higher efficiencies, the size of the outdoor coil (i.e., the tubular assembly) increases. To keep the overall size of the outdoor coil within a reasonably sized package, sometimes a second coil is added to the outdoor coil. The second coil can be wound around the first, as disclosed in U.S. Pat. No. 4,554,968, or the second coil can be slightly smaller than the first and slipped inside the outer one. Either way provides an outdoor heat exchanger with two rows of coils: an inner one and an outer one.
Although a conventional heat exchanger coil with two rows is quite efficient, several problems are associated with such a coil. First, some double-row coils require a tubing connection, or jumper, to connect an inner coil to an outer one. Such a connection is commonly made by cutting both coils, pulling part of the inner coil through the outer one, and then connecting the two with a U-shaped return bend. When the return bend is copper and the coil tubing is aluminum, a transition joint may also be necessary. Each connection adds assembly time and increases the likelihood of leaks. Moreover, wherever the coil is cut to attach either a manifold or a jumper, a hole is left through which air flows, bypassing the coil and avoiding heat exchange.
Second, inner coils are typically large and unwieldy, which make them difficult to insert into an outer coil.
Third, the coil configuration of conventional double-row coils tends to dictate the location of the manifolds (e.g., both on the inside, both on the outside, or one on each side), regardless of other design criteria. However, it may be preferable to have the manifold in another location for other reasons, such as ease of assembly (e.g., both manifold on the outside) or compactness (e.g., both manifolds on the inside).
Fourth, for many double-row coils most of the inner loops (i.e., inner passes) are closer to the vapor connections with respect to refrigerant flow than the liquid connections, as is the case with the U.S. Pat. No. 4,554,968. The terms, xe2x80x9cvapor connectionxe2x80x9d and xe2x80x9cliquid connectionxe2x80x9d are relative in that the refrigerant normally tends more toward the liquid state at the liquid connection than at the vapor connection. However, the refrigerant is not necessarily a liquid, gas, or any particular combination of the two at either connection. For example, an individual wound tube of the outdoor coil runs between a vapor connection at one manifold and a liquid connection at another manifold. When the outdoor coil functions as a condenser in a system operating in a cooling mode, the refrigerant tends to give off heat and condense as it flows from the vapor connection to the liquid connection. And for that same outdoor coil functioning as an evaporator when the system is in a heating mode, the refrigerant tends to a more gaseous or superheated state as the refrigerant absorbs heat upon flowing in reverse from the liquid connection to the vapor connection. With the system operating in the heating mode, the loops near the vapor connection typically convey superheated refrigerant. The problem here is that significantly more coil area is required to reach a given level of superheat if the superheating passes are on the inner row, since the difference between the refrigerant temperature and the outdoor air temperature here is slight. Also, since a large portion of the coil""s refrigerant-side pressure drop occurs in the superheating region, more coil area in superheat means more refrigerant-side pressure drop and worse performance. Nonetheless, of the five circuits of the coil disclosed in the U.S. Pat. No. 4,554,968, only one (the bottom one) transits from an outer loop to an inner one, and then it only transits once.
Fifth, in manufacturing a multi-circuit, coiled heat exchanger, it is often preferable to first wrap the entire coil as a single circuit and later cut the continuous coil into smaller circuits. This avoids slowing the coiling process by having to repeatedly interrupt a power coiler, such as those similar to the one disclosed in U.S. Pat. No. 5,737,828. However such an approach is not always practical, especially when the coil configuration fails to position the liquid loop of a first circuit closer to the vapor loop of an adjacent circuit than to the vapor loop of the first circuit, as appears to be the case in the U.S. Pat. No. 4,554,968. Placing the liquid loop of a first circuit adjacent or near the vapor loop of an adjacent circuit allows two ends of each loop to be created with a single tube cut.
Just as the terms, xe2x80x9cvapor connectionxe2x80x9d and xe2x80x9cliquid connection,xe2x80x9d are used in a relative sense, other terms such as xe2x80x9cvapor loop,xe2x80x9d xe2x80x9cvapor manifold,xe2x80x9d xe2x80x9cvapor connection,xe2x80x9d xe2x80x9cliquid loop,xe2x80x9d xe2x80x9cliquid manifold,xe2x80x9d xe2x80x9cliquid connection,xe2x80x9d etc., are also used relatively in that the refrigerant tends more toward the liquid state in the liquid manifold, liquid loop, and liquid connection than in the vapor manifold, vapor loop, and vapor connection respectively.
A sixth problem with many conventional double-coil heat exchangers is that most of the hot discharge refrigerant gas used for defrost cools significantly upon first passing through the inner coil before reaching the outer one. For example, the U.S. Pat. No. 4,554,968 appears to show refrigerant in a defrost cycle having to pass through at least three inner loops before transiting to an outer loop. But often most of the frost tends to accumulate on the outer coil where the outdoor air enters the coil. Consequently, hot defrost refrigerant having to first pass through several inner loops before reaching an outer one tends to extend the defrost cycle and degrade the heating efficiency of the system.
Seventh, the maximum outdoor air velocity across a heat exchanger having a uniform distribution of coils usually occurs near the fan inlet, somewhere between the top and bottom of the coil. The airflow velocity at the top and bottom of the coil is generally lower, and thus those areas are not used as effectively as the area near the fan inlet.
To overcome the numerous problems and limitations of conventional heat exchangers with two rows of coils, it is an object of the invention to intertwine the inner and outer coils.
Another object of the invention is to provide a double-coil heat exchanger with several parallel-flow circuits that can be wound in a single, continuous winding operation and yet still position vapor and liquid connections at strategic locations, e.g., a liquid loop of a first circuit being closer to a vapor loop of an adjacent circuit than a vapor loop of the first circuit.
Another object is to provide a double-coil heat exchanger with several parallel-flow circuits that can be wound in a single, continuous winding operation, while allowing a generally single tube cut to provide both a vapor and liquid connection that are cicumferentially positioned within the same quadrant of a coil.
Yet another object is to provide a double-coil heat exchanger with several vapor and liquid connections that are readily positioned for connection to two manifolds at optional locations: both inside an inner coil, both outside an outer coil, or one inside and one outside.
A further object is to employ an inner or outer loop to obstruct an otherwise open hole at a tubing connection.
A still further object is to intertwine the inner and outer coils of a heat exchanger to alternate the defrost and/or superheating passes.
Another object of the invention is to provide a double-coil heat exchanger with a single row of coils at the upper and/or lower end of the heat exchanger to more evenly distribute the airflow across the coils.
Another object is to interrupt the second row of a double-coil heat exchanger at a vapor pass (i.e., loop or pass adjacent a vapor connection) to maximize the vapor loop""s exposure to airflow.
Another object is to provide a double-coil heat exchanger having a minimum number of jumpers, such as couplings and return bends.
Yet another object is to provide a double-coil heat exchanger while avoiding the challenge of slipping one coil inside an outer one.
In some embodiments, another object is to vertically stagger the inner and outer loops of a double-coil heat exchanger to minimize the overall size of the heat exchanger.
In some embodiments, another object is to vertically align the inner and outer loops of a double-coil heat exchanger, so that when winding both coils in a single operation, the inner loops firmly support the outer loops. This prevents the outer loops from squeezing between the inner loops which tends to happen when the inner and outer loops are vertically staggered.
The present invention provides a heat exchanger coil. The coil comprises a circuit-A extending in a coiled configuration from a vapor loop-A to a liquid loop-A and being distributed to create a plurality of inner A-loops and a plurality of outer A-loops. The circuit-A repeatedly transits from the plurality of outer A-loops to the plurality of inner A-loops, as the circuit-A runs from the vapor loop-A to the liquid loop-A.
The present invention additionally provides a heat exchanger coil. The coil comprises a circuit-A extending from a vapor loop-A to a liquid loop-A and being distributed to create a plurality of inner A-loops and a plurality of outer A-loops; and a circuit-B in parallel-flow relationship with said circuit-A and extending from a vapor loop-B to a liquid loop-B. The circuit-B is distributed to create a plurality of inner B-loops and a plurality of outer B-loops with the liquid loop-A being closer to the vapor loop-B than the vapor loop-A.
The present invention also provides a refrigerant system. The system comprises a refrigerant compressor; a flow restriction; an indoor heat exchanger; an outdoor heat exchanger that includes a vapor manifold and a liquid manifold that place the outdoor heat exchanger in series flow relationship with the refrigerant compressor, the flow restriction and the indoor heat exchanger. The system also comprises a circuit-A borne by the outdoor heat exchanger and extending from a vapor loop-A to a liquid loop-A with the vapor loop-A being coupled to the vapor manifold and the liquid loop-A being coupled to the liquid manifold. The circuit-A is distributed to create a plurality of inner A-loops and a plurality of outer A-loops and repeatedly transits from the plurality of outer A-loops to the plurality of inner A-loops, as the circuit-A runs from the vapor loop-A to the liquid loop-A. The system also comprises a circuit-B borne by the outdoor heat exchanger and extending from a vapor loop-B to a liquid loop-B with the vapor loop-B being coupled to the vapor manifold and the liquid loop-B being coupled to the liquid manifold to place the circuit-B in parallel flow relationship with the circuit-A. The circuit-B is distributed to create a plurality of inner B-loops and a plurality of outer B-loops with the liquid loop-A being closer to the vapor loop-B than the vapor loop-A. The circuit-B repeatedly transits from the plurality of outer B-loops to the plurality of inner B-loops, as the circuit-B runs from the vapor loop-B to the liquid loop-B.
The present invention further provides a heat exchanger coil comprising: a first vertically aligned row of spine fin tubing; a second vertically aligned row of spine fin tubing; and circuiting to repeatedly transit the flow of a fluid between the first and second rows.
These and other objects of the invention are provided by double-coil heat exchanger having inner and outer loops that are intertwined such that the outer loop repeatedly transits to the inner loop.